The present invention relates to a closed loop control scheme for a rotating system. In particular, it relates to a temperature regulation scheme, whereby a constant current signal proportional to the temperature within a rotating drum is produced and coupled to a remote stationary controller that synchronously supplies power to heater elements within the rotating system.
A problem attendant with heat controllers for rotating heating systems is that of not being able to accurately, and in a cost effective manner, sense temperature and control the switching of power to the heating elements. Heretofore, a number of different techniques have been employed, and the most pertinent of which can be found upon reference to U.S. Pat. Nos. 3,637,984; 4,097,723; 3,674,963; 3,278,723; and 4,127,764. These patents generally show various electro-mechanical combinations that employ slip rings and/or inductive coupling or photo conductive coupling of control signals and/or switch power to the heater elements via pulse width modulation or frequency comparison techniques.
With reference to U.S. Pat. No. 4,114,023, which is assigned to the present assignee, there is described an open-loop control arrangement. It too does not suggest the present, improved, closed-loop scheme. Thus, nowhere, in the prior art of which we are aware is a closed-loop control system shown for generating a constant current signal proportional to the temperature within a rotating drum along with means for transmitting the current signal to a stationary controller, whereat the current signal is compared to a set-point signal and the zero-crossing of the line voltage so as to synchronously switch a triac type semiconductor switch and supply power to the heating elements, when the temperature within the drum falls below the set-point.
The above advantage and those various other advantages and objectives that are achieved via the present invention will, however, become more apparent upon a reading of the following description and upon reference to the following drawings.